1. Field of the Invention
The present invention relates to zoom lenses, more particularly though not exclusively, to zoom lenses used in image-pickup apparatuses.
2. Description of the Related Art
Recently, image-pickup apparatuses, such as a photographic camera, a video camera, and a digital camera, have been demanded to have higher quality images.
Furthermore, because of the expansion in shooting conditions, it would be useful for the lenses used in these apparatuses to be zoom lenses having image stabilizing performances for correcting blurring due to camera shake.
A method of compensating vibration includes decentering selected lens groups arranged in parallel with a direction substantially perpendicular to an optical axis. This method needs no additional optical system for compensating vibration.
This method also has merits that the lens groups for vibration compensating can be mostly simplified and an actuator for vibration compensating can be miniaturized by suppressing a drive torque.
On the other hand, there is a so-called negative lead type zoom lens in that a lens group with negative refractive power is preceding (located at a position closest to an object). In this zoom lens, a distance of contact shooting is comparatively small, a shooting field angle can be increased rather easily, and a back focus can be increased comparatively easily so as to be frequently used in a wide-field angle taking lens.
A two-group zoom lens composed of first and second lens groups with negative and positive refractive power arranged from the object in that order, has been known as the negative lead type zoom lens having image stabilizing performances (Japanese Patent Laid-Open No. 10-161024 and No. 7-64025). In this two-lens group, the vibration is compensated by moving part of the second lens group in a direction substantially perpendicular to the optical axis.
Also, a four-group zoom lens, composed of first to fourth lens groups with negative, positive, negative, and positive refractive power arranged from the object in that order, has been known, in which the vibration is compensated by moving part of the second lens group in a direction substantially perpendicular to the optical axis (Japanese Patent Laid-Open No. 9-113808 and No. 2004-61910).
In the two-group zoom lens discussed in Japanese Patent Laid-Open No. 10-161024 and No. 7-64025, the variable power is given only to the second lens group. Hence, when the lens is zoomed at a high ratio, the variations in aberration due to the zooming are difficult to be suppressed.
Since the displacement of the second lens group during zooming is comparatively large relative to the zoom ratio, the entire lens system is difficult to be miniaturized.
The vibration is compensated by parallel decentering part of the second lens group; however, when the lens is zoomed at a high ratio, the increasing tendency of aberration due to the vibration compensating has been shown.
In the four-group zoom lens discussed in Japanese Patent Laid-Open No. 9-113808 and No. 2004-61910, the vibration is compensated by moving a plurality of lenses in a direction substantially perpendicular to the optical axis, so that the weight of the moving part is increased and the lens frame therefore is also increased in size. Thus, a large load is applied to a drive system for correcting the blurring (compensating the vibration), resulting in an increasing tendency in size of the camera shake drive system.
When the vibration is compensated by decentering the lens, there can be a delayed response in decentering the lens.
In the zoom lens having a image stabilizing mechanism for use in a high quality image-pickup apparatus, it would be useful that the lens for correcting the image blur is small in size and weight and the deterioration in optical performances is small during compensating the vibration.